public class Solution {
    public static int numDistinct(String s, String t) {
        int len1 = s.length();
        int len2 = t.length();

        char[] ch1 = s.toCharArray();
        char[] ch2 = t.toCharArray();

        int[][] dp = new int[len1 + 1][len2 + 1];
        for (int i = 0; i < len1 + 1; i++) {
            dp[i][0] = 1;
        }

        int ret = 0;
        for (int i = 1; i < len1 + 1; i++) {
            for (int j = 1; j < len2 + 1; j++) {
                dp[i][j] = dp[i - 1][j];
                if (ch1[i - 1] == ch2[j - 1]) {
                    dp[i][j] += dp[i - 1][j - 1];
                }
                // ret += dp[i][j];
            }
        }

        return dp[len1][len2];
    }

    public static void main(String[] args) {
        System.out.println(numDistinct("rabbbit", "rabbit"));
    }
}
